Selective demethylation of paraffing hydrocarbons



treatment.

Patented June 24, 1947 q "UNITED. STAT PATENTS OFFICE SELECTIVE DEMETHYLA'TION F,

PAR

side, 11]., assignors "name This invention relates'to the preparationgof' hydrocarbons having a, shorter carbon chain from a hydrocarbon havinga longer carbon chain, the hydrocarbon with longer chain containing at least one carbon atom more than'th'ose present I [inthe hydrocarbon-s produced therefrom. More specifically, the invention is concernedwith a process for. treating an aliphatic hydrocarbon containing a quaternary carbon atom to. effect selective demethylation and produce a saturated hydrocarbon of lower molecular weight containing a quaternary carbon atom.

In one specific embodiment the present invention comprises aprocess for treating withhydrogen a parafiinic hydrocarbon having a quatere nary carbon atom to produce therefrom a hydrocarbon of lower molecular weight also containing 7 a quaternary carbon atom.

Heretoiore destructive hydrogenation methods have been utilized in producing gasoline from higher boiling oils in the presence of various hydrogenating catalysts. Such a process may be regarded as a cracking of the higher boiling oils accompanied by hydrogenation of the resultant products of lower molecularweight to form sub-" stantially saturated hydrocarbons boiling within the range of gasoline. The present process diflers.

from the destructive hydrogenation methods of the prior art in that it specifically involves demethyiation, and also in the nature of the chargingstock, the particular and specific conditions oftoperation necessary to effect theherein dethe products which havehighly branched chain structures and highantiknock values.

By the term selective demethylation we mean the herein described treatment of an aliphatic hydrocarbon with hydrogen in the presence of a catalyst wherebycertain methyl groups are removed in preference to other groups from a hydrocarbonmolecme being subjected to said For example, neohexane, which has (CH3):--C-CH2CH3, has four terthe formula I initial. methylgroups, three of which groups are combined withfthe quaternary carbon atom and the remaining methyl group is. a part of the ethyl group of the neohexane molecule. Accordingly if any one of the methyl groups attached to the quaternary carbon atom is removed therefrom under hydrogenating conditions, methane Vladimir Haensel and t:

' pentyl group and the tane resultsiin the removal c nrnaooaanons adimir N. Ipatiefl, River-- Universal Oil Products Company, Chicago, Ill., a corporation of Dela- Applicationjebruary 6,1943, serial No. 475,004

14ClaimtiClg60+683.6)- 7' Y t and. isofieiitanejrill be formed while the similar splitting-off of the other methyl group which is a portion of the ethylgrouoof the neohexane molecule would result in the formation of methane and neopentane. Accordingly, if allotthe bonds between the diifere t carbon atoms'of the neohexane molecule are of equal strength, the probability of isopentaneformation is three times that of neopentane production. However, we have found experimentally that the bonds between the carbon atoms of the neopentylgroup are stronger than is the bond between: the neoterminal methyl group of the neohexane molecule. The experimental evidence shows that in this treatment neopentane production is 5.4,timesgreater than the produc-. tion orisopentane. v

Similar demethylation of 2,2,4-trimethyl penas methane of methylgroups bound to carbon atoms other than the quaternary carbon atom. Thus, this particular iso-octane undergoes selective demethylatiorgl?) V and 2,2'- dimethy1 pentane, which may be referred to as neoheptane. Such formation of neoheptane and neohexane is accompanied by the production or methaneby scribed selective demethylation process, and also certain nonanes and other hydrogenation of the one or so removed from 2,2,4-trimethyl pentane.

We have also found that triptane, more exactly known as 2,2,3-trimethyl butane, is also produced in substantial yield by treating: 2,2;35' trimethyl' pentane according to the process, of our invention. Triptane is also producible byour.

process from 2,3,3-trimethy1 pentane and from hydrocarbons 0011-! taining a triptyl group. Such hydrocarbon starting materials contain adjacent quaternary and tertiary carbon atoms, that is one carbon atom is combined chemically with four other carbon atoms and one of said four carbon atoms is tertiary in that it is bound to the quaternary carbon atom, to two other carbon atoms, and to only onehydrogen atom.

According to our invention, it i possible to selectively remove methane from a hydrocarbon containing a triptyl structure so as to produce a lower molecular weighthydrocarbon containing only a quaternary carbon atom, a tertiary carbon atom, and the other carbon atoms bound two methyl groups 1 v r 3 directl to said quaternary and tertiary carbon atoms. This process sheets the selective removal of methane usually from the longest and least branched alkyl group which is bound to the quaternary or tertiary carbon atoms of the hydrocarbon.

The hydrocarbon which is submitted to demethylation treatment may also contain more than one tertiary carbon atom.

The selective demethylation treatment-of ali-.

phatic hydrocarbons containing aquaternary carbon atom may be carried out either continuously or in batch type operation in the presence of a hydrogenating catalyst at a temperature of from about 175 to about 375 C. and under a pressure of from substantially atmospheric to approximately 300 atmospheres. Suitable cata- .bons may be carried out in reactors or autoclaves oi. suitable design in which the hydrocarbon charged and catalyst may be contacted with hy drogen or a hydrogen-containing gas mixture under the desired conditions of operation and for I pressure. Thus, the reaction products are conlysts comprise the metals oftheiron group and I their oxides including iron, nickel, and-cobalt used as such or supported by carriers; and also the noble metals platinum and palladium. Under ,1

some conditions of operation selective demethyla-f tion may also be eil'ected in the presence o f an oxide or sulfide of a metal of the left-handcolumn/"" of.Group 6 of the Periodic Table includingchTomium, molybdenum, and tungst i /K 1 A highly active nickel catalyst which we have used in 'demethylation treatment ofparafilns contains; ap mx'imfle y 66% V by weight of total nickel; 30%"ot 'diatomaceous earthjand 4% of oxygen, *the latter" present with nickel as nickel oxide. "This catalyst is'made bythe general stepsofsuspending diatomaceous earth, also known as' kieselguhr, in a dilute aqueous solution of nickel sulfateand then gradually adding thereto an excess of ahot saturated solution of sodium carbonate. The mixture'of nickel sulfate solution and" diatomaceous earth is agitated I vigorously whilethe'sodium'carbonate solution is introduced theret'o'to'iorm a precipitate which is then re-' movedby filtration, washedfdried, and reduced with hydrogen. a r V i a The'particular o'perating'conditionsof temperature'and pressure utilized in thepresent process are dependent-upon the hydrocarbon or hydro carbon'mixture being treated, the composition and activity of thecatalyst, the ratio of hydrogen. to hydrocarbon, and other factors. Furthermore, the difl'erent hydrocarbon which maybe subjected to hydrogenation to split methane therefrom and form substantially saturated hydroc'arbons 0t lower molecular weight are not necessarily equivalent in their behavior under conditions of-selective 'demethylation.

It is'sometimes advantageous to commingle the hydrogenfwith methane or some others'ubstantially inertgas in order to control the reaction temperature and the extent orthe demethylation reaction. Proper control'of the demethylation'reaction isdesirableandnecessary as otherwise the desired products ofthe process undergo further demethylation to lower molecular weight paraflins. Such control of the demethylation process may be accomplished by'regulating the partial pressure of the hydrogen in the system, forexample by recycling a portion of the methane or methaneehydrogen mixture coming from the processor by mixing with the hydrogen controlledamounts of some other inert gas. The ratio of hydrogen to methanemaybe adjusted so as to assist in controlling the temperature of the catalyst uponwhich considerable heat or reaction is liberatedbecause of the highly exothermic nature of thedemethylation reaction.

tinuously. discharged from the reactor at substantially the rate at which they are charged thereto. Theproducts of the selective demethyl- .ation treatment are fractionated by suitable means to separate the desired lower b'oil ingmydrocarbons from the uncpnverted'port'ro'n of the hydrocarbon materiaYch arged to the process, and

. said' 1 ic9nverted portionbf hydrocarbon mate- Batch type treatmentor aliphatic hydrocar rial is-recycledto c ommingle with the hydrocarbon material charged to the process.

, The process is not limited to any particular type of apparatus and depends for its successful operation upon the use of particular'temperatures along with proper pressures and timesof contact suitable to the different demethylation" catalysts utilized.

The following examples are given to illustrate the process of the invention, although with no intention of unduly limiting its generally broad scoper i EXAMPLE I A catalyst containing approximately'66% by Weight of total nickel, 30% of diatomaceous earth, and 4 of oxygen in the form of nickel oxide was prepared by suspending diatomaceous earth in a dilute aqueous solution of nickel sulfate and then gradually adding thereto with vigorous agitation an excess of a hot saturated solution of sodium carbonate to form a Precipitate consisting essentially of nickel carbonate mixed with diatomaceous earth. The resultant mixture of precipitate and diatomaceous earth wash filtered from the mother liquor, washed, dried, and reduced with hydrogen to form an active catalyst.

35 parts'by weight of neohexane and 8 parts by weight ofthe above described reduced nickel-l diatomaceous earth catalyst were placed in a rotatable steel autoclave, hydrogen was introduced to a pressure of atmospheres and the resultant mixture was heated at a temperature 01 between 260 and 275 C. for 4.5 hours. After this treatment the autoclave was cooled to room temperature and about 30 parts by weight of liquid products were removed therefrom. Fractional distillation separated these liquid products into 1.5 mole per cent of butane, 9.6% of neopentane, 1.8% of isopentane, 1.4% of normal pentane, 83.7% of unconverted neohexane,'and 2% by weight of higher boiling materials. A 59 mole per cent yield of neopentane was thus obtained upon the basis of the neohexane which underwent conversion. There was also about a' 20% yield of a mixture or isopentane and normal pentane while butane production was equivalent to about-9% of the neohexane converted.

EXAMPLE II Mixtures of neohexane and hydrogen were passed continuously under atmospheric pressure through cylindrical reactor containing '3 x 3 mm. cylindrical particles of the nickel-kieselguhr Catalytic partial demethylation of neohemane in I the presence of hydrogen Run No 1 2 3 4 Catalyst reactor temp, "C 215 225 226 253 Duration of run, minutes 6O 45 60 45 Neohexane charging rate, vol. per hour per vol. of catalyst 0.57 l 2 0.57 l. 2 Molar ratio of hydrogen to neohexane chg 2. 6 2. 5 2. 5 2:7 Moles of hydrogen chgd 0.85 0. 63 0.80 0. 67 Liquid product, wt. per cent of noohexane chgd 97. 94 42. 40. l Non-condensible gas, moles 0.87 0.65 '1. 0 0.87 Analysis of liquid product, mole per cent:

Butanes 0.2 0.5 2.9 1.2 Neopentane 4:5 4. 3 21. 1 20:8 isoand n-pentanes 1.0 0.5 0.5 0.0 Neohexane .1 94.0 94. 7 75. 5 78. 0 Analysis of non-condensihle gas, mole per J 3 oen V Hydrogen 96. 0 94. 3 2. 7 2. i Methane 4. 0 5. 7 -96.8 97. 9 Ultimate yield of neopentane, mole per 1 cent of neohexane charged 50 39 31 39 The results given inthe above table show, that the selective demethylation reaction requires careful control of, operating conditions in order to,

produce-substantial yields. of neopentane andv to suppress excessive formation of methane. At a reactor temperature of 215 C. andunder atmos pheric pressure about 50 'mole per cent of the neohexane which reactedyielded neopentane. ,At a higher temperature, as at 225-2269 0., the

amount of neoh'exane converted per pass was dependent upon the rate at which this hydrocarbon was charged to the process. When 1.2 volumesof neohexane was charged per hour per volume of catalyst, the recovered liquid product containing about 4.3 mole per cent of neopentane corresponded to an ultimate or recycle yield of.39%. However, when 0.57 volume ,of neohexanewas charged per hour per volume of catalyst in run 3, the recovered liquid product contained 21-,mole per cent of neopentane but this yield correspondedto only about 31% of the-theoretical based upon the amount ofneohexane undergoing conversion. Run 4 which was made ata reactor 250 cc. of an octane mixture containing about 85% of 2,2,3-trimethyl pentane and about of 2,2,4- and 2,3,4-trimethyl pentanes was subjected to the action of hydrogen at 300 C. for 4 hours in the presence of 20 grams of the catalyst described in Example I. In this run the octane mixture was charged to a rotatable steel autoclave of 850 cc. capacity to which hydrogenwas then introduced to 100 atmospheres initial pres;

sure.

After the autoclave and contents; had been heated as aforementioned, the autoclave was then permitted to cool and the residual gases were released and analyzed. This residualgas contained 0.2% by volume of oxygen, 0.2% carbon monoxide, 88.1 %1hydrogen, 8.5% of methane, and 3% of nitrogen.

After the gas was released, 235 cc. of liquid product was recovered from which, the catalyst was removed by filtration. Fractional distillation of the filtered liquid product separated therefrom a fraction of 16 cc. of heptanes containing at least by volume of triptane. Intermediate fractions containing approximately 60% of triptane were also obtained which increased the yield of tri'ptane to 8.4% based upon the octane mixture charged to the autoclave. Besides containing triptane, the recovered liquid product consisted essentiallyof unconverted octane fraction suitable for recycling'to further demethylation treatheptanes calculated from the formation of methane by assuming that the demethylationof one molecular proportion of octane yielded one molecular proportion each of heptane and methane.

Previous freezing point tests on synthetic mixtures containing 85% by volume of triptane' and 15%" of 'either 2,2- or 2,4-dimethyl pentanes,

which have boiling points close to that of triptane,

showed'that such mixtures become solid at '18 C. Thepresence in triptane of larger. amounts of these other heptanes resultsin mixtures-which do not become solid at -'78 C. The 16 cc; fraction of heptanes obtained in the abovementioned run solidified completely when cooled to 78 C. and therefore is considered to contain at least 85% of triptane. Additional proof that triptane was present in this fraction was obtained by brominating it in the presence of light to give a solid monobromide melting at 152 C. which is the melting point of the monobromide similarly obtained from synthetically prepared triptane. Also when the monobromide prepared from the fraction of a demethylation product was mixed with triptyl .bromide, a mixed melting pointof 152-153" C. was obtained, thus proving the presence of tript'ane in the products formed by'subjecting 2,2,3-trimethyl pentane to hydrogenation treatment. Y Y

EXAMPLE IV an octane'mixture containing approximately 70% of 2,2,3-trimethyl pentane and 30% of 2,3,4- trimethylpentane was used as charging stock in another run carried out in the same autoclave referred to-in Example III. In this run 250 cc.

of the'oc'tane mixture and 40 grams of the catalyst "described in Example I were placed in the autoclave and hydrogen was introduced thereto toaninitial pressure of atmospheres. 'I he autoclave so charged was then rotated and heated at 300 C. for 6 hours under a maximum pressure of 200 atmospheres. The autoclave and contents were then cooled to room temperature, the resid- Percent by volume Hexanesu 4.7 Triptanefl' 19.9 2,3-dimethyl pentane 8.2 2,2,4-trimethyl pentane 3.5 Unconverted octanes '59.? Volume loss 4 comprising essentially a mixture of triptane and 2,3-dimethyl pentane obtained in thisrun gave a 40 cc. fraction, which upon the basis of its melting point, was estimated to contain about 97% by volume of triptane.

The foregoing specification and examples indicate the character and value of the present process, although it is not intended that either section should unduly limit the generally broad scope of the invention. a

We claim as our invention:

1. A process for demethylating 2,2,3 trimethylpentane which comprises commingling the 2,2,3 trimethylpentane with hydrogen in the amount of at least about 1.6 mols of hydrogen per mol of 2,2,3 trimethylpentane subjecting the resultant mixture to reaction at a temperature of from about 175 toabout 375 C. and apressure of from atmospheric to about 300 atmospheres in the presence oi a hydrogenating catalyst and 'cora I 8 radical of at least two carbon atoms, which comprises commingling said paraflin with hydrogen in the amount of at least about 1.6 mols of hydrogen per mol of the paraffin, subjecting the resultant mixture to reaction in the presence of a hydrogenating catalyst at a temperature of from about 175 C. to about 375 C. and under a pressure of from atmospheric to about 300 atmospheres to replace with hydrogen the terminal methyl group of said alkyl radical of the paraflin molecule, terminating the reaction of hydrogen with said paraflin prior to the splitting from the paraffin molecule of an alkyl group or more than one carbon atom and of any of the methyl radicals attached to said quaternary carbon atom, whereby to lower the number'of carbon atoms of the paraflin molecule solely by demethylation of said alkyl radical while retaining the quaternary carbon atom configuration of the paraflin molecule, and recovering as the principal product of the proces the resultant demethylated paraffin having the quaternary carbon atom configuration.

5. A process for producing neopentane from a paraflin containing a, quaternary carbon atom having attached thereto three methyl radicals and an ethyl radical, which comprises commingling said paramn with hydrogen in the amount of at least about 1.6 mols of hydrogen per mol of the paraffin, subjecting the resultant mixture to reaction in the presence oi! a hydrogenating catalyst at a temperature of from about 175 C. to about 375C. and under a pressure of from atmospheric to about 300 atmospheres to relating the mol ratio of hydrogen to 2,2,3 trimethyipentane and the temperature and pressure to remove the and methyl radical not attached to either the quaternary or tertiary carbon atoms of said 252,3 trimethylpentane whereby to form triptane as the principal reaction or the process.

2. A, process for producing a lower molecular weight saturated hydrocarbon from a paraflln containing a quaternary carbon atom having attached thereto an' alkyl radical of at least two carbon atoms, which comprises commingling said paraflln with hydrogen in the amount of at least about 1.6 mols of hydrogen per mol of the paraffin, subjecting the resultant mixture to reaction in the presence of a hydrogenating catalyst at a temperature of from about 175 C. to about 3759 C. and under a pressure of from atmospheric to about 300 atmospheres to replace with hydrogen the terminal methyl group of said alkyl radical of the paraffin molecule, terminating the reaction of hydrogen with said parafiin prior to the splitting from the paraflln molecule of an alkyl group of more than one carbon atom and prior to scission of any of the bonds of said quaternary carbon atom, whereby to lower the number of carbon atoms of the paraiiln molecule solely by demethylation while retaining its quaternary carreplace with hydrogen only the terminal methyl group of said ethyl radical of the paraffin molecule, terminating the reaction of hydrogen with said paraffin prior to scission of any of the bonds of said quaternary carbon atom, whereby to lower the number of carbon atoms of the paraflln molecule solely by removal of said terminal methyl group while retaining the quaternary carbon atom configuration of the paraffin molecule, and recovering as the principal product of the process the resultant demethylated paraffin containing the quaternary carbon atom having four methyl groups attached thereto.

6. A process for producing triptane which comprises commingling 2,2,3-trimethylpentane with hydrogen in the amount of at least about 1.6 mols of hydrogen per mol of said hydrocarbon, subjecting the resultant mixture to reaction in the demethylated parailln having the quaternarycar- I bon atom configuration.

3. The process of claim 2 further characterized in that said hydrogenating catalyst comprises a metal of the iron group of the periodic table of the elements.

- 4. A process for producing a lower molecular weight saturated hydrocarbon from a paraflin containing a quaternary carbon atom having attached theretothree methyl radicals and an alkyl presence of a hydrogenating catalyst at a temperature of from about 175 C. to about 375 C.

and under a pressure of from atmospheric to about 300 atmospheres to replace with hydrogen the terminal methyl group not attached to the quaternary or tertiary carbon atom of the hydrocarbon molecule, terminating the reaction of hydrogen with said hydrocarbon prior to the splitting from the latter of any alkyl group other than said terminal methyl group, whereby to lower by one the number of carbon atoms of the hydrocarbon molecule while retaining the adjacent quaternary and tertiary carbon atom configuration of the hydrocarbon molecule, and recovering as the principal product of the process the resultant demethylated paraflin having adjacent quaternary and tertiary carbon atoms.

7. The process as defined in claim 2 further characterized in that said catalyst comprises nickel. I

8. The process as defined in claim 5 further characterized in that said catalyst comprises nickel.

9 characterized in that said catalyst comprises nickel,

10. A process for producing a lower molecular weight saturated hydrocarbon from a paraflin containing a quaternary carbon atom having attached thereto an alkyl radical of at least two carbon atoms, which comprises commingling said paraflin with hydrogen in the amount of at least about 1.6 mols of hydrogen per mol of the paraifin, subjecting the resultant mixture to reaction in the presence of a hydrogenating catalyst at a temperature of from about 175 C. to about 375 C. and under a pressure of from atmospheric to about 300 atmospheres to replace with hydrogen the terminal methyl group of said alkyl radical of the paraffin molecule, correlating said temperature and pressure to prevent the splitting from the paraflin molecule of an alkyl group of more than one carbon atom and the scission of any of the bonds ofsaid quaternary carbon atom, whereby to lower the number of carbon atoms of the paraifin molecule solely by demethylation While retaining its quaternary carbon atom configuration, and recovering as the principal product of the process the resultant demethylated paraffin having the quaternary carbon atom configuration. I

11. The process as defined in claim 10 further characterized in that said paraflin is a trimethylpentane.

12. The process as defined in claim 10 further characterized in that said parafiln is 2,2,3-trimethylpentane.

13. The process as defined in claim 10 further characterized in that said parafi'in is neohexane.

14. A process for producing a lower molecular weight saturated hydrocarbon from a paraffin containing a quaternary carbon atom having attached thereto an alkyl radical of at least two carbon atoms, which comprises commingling said 10 paraflln with hydrogen in the amount of at least about 1.6 mols of hydrogen per mol of the paraflin, subjecting the resultant mixture to reac tion in the presence of a hydrogenating catalyst at a temperature of from about 205 C. to about 350 C. and under a pressure of from 15 to about 3000 pounds per square inch to replace with hydrogen the terminal methyl group of said alkyl REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,214,463 Ipatiefi et a1 Sept. 10, 1940 2,259,862 Ruys et a1. Oct. 21, 1941 2,322,863 Marschner June 29, 1943 1,960,206 Edmonds May 22, 1934 2,270,303 Ipatieff Jan. 20, 1942 OTHER REFERENCES Otuka et al., Journal of the Society of Chemical Industry, Japan, vol. 43, No. 12, pages 454B to 4563, December, 1940. (Copy in Division 31 at 196-53.) 

